Re: issue trying to query wikidata with jena api

[Andy Seaborne]

The URL is sending back HTML.

Probably means it is a URL to a form for asking SPARQL queries, not the 
SPARQL endpoint itself.  See if you can find out where the form sends 
the query.

    Andy

On 09/04/2020 14:29, Luis Enrique Ramos García wrote:
Andy,

In addition I am working in another end point, and now I am getting this
output:

Endpoint returned Content-Type: text/html which is not rcognized for SELECT
queries

I followed this recommendation

https://stackoverflow.com/questions/41926530/jena-endpoint-returned-content-type-text-html


however the behavior does not change, and I continue receiving this error:

Exception in thread "main" org.apache.jena.query.QueryException: Endpoint
returned Content-Type: text/html which is not rcognized for SELECT queries
at
org.apache.jena.sparql.engine.http.QueryEngineHTTP.execResultSetInner(QueryEngineHTTP.java:377)
at
org.apache.jena.sparql.engine.http.QueryEngineHTTP.execSelect(QueryEngineHTTP.java:345)
at
ag.pst.jena.test.RDFConnectionExample4.main(RDFConnectionExample4.java:84)

any recommendation?


Luis

El jue., 9 abr. 2020 a las 15:03, Andy Seaborne (<a...@apache.org>)
escribió:

     "SELECT ?item1  WHERE {\n" +
     "    ?item1 wdt:P31 ?item2.\n" +
     "} LIMIT 10";


qs1.getResource("s")

The variable is called "item1"

      qs1.getResource("item1")

   Andy

On 09/04/2020 13:47, Luis Enrique Ramos García wrote:
dear member of jena community,

I have been trying to query wikidata following the documentation [1] and
other examples I have found, but result obtained has been null values,
besides it is a simple query, that I have just previously tested in the
wikidata query GUI.

I followed two methods, one with  QueryExecution, and another
with RDFConnectionRemote, but however in both the output is null as well.

Please, let me know if I am missing something, or if I am going in the
wrong direction.


Best regards



Luis Ramos


*CODE *



import org.apache.jena.query.Query;
import org.apache.jena.query.QueryExecution;
import org.apache.jena.query.QueryExecutionFactory;
import org.apache.jena.query.QueryFactory;
import org.apache.jena.query.QuerySolution;
import org.apache.jena.query.ResultSet;
import org.apache.jena.rdf.model.Resource;
import org.apache.jena.rdfconnection.RDFConnection;
import org.apache.jena.rdfconnection.RDFConnectionFactory;
import org.apache.jena.rdfconnection.RDFConnectionRemote;
import org.apache.log4j.BasicConfigurator;
import org.apache.log4j.Level;
import org.apache.log4j.Logger;




/*
   * Example of a building a remote connection.

   */
public class RDFConnectionExample4 {

//testing
static Logger log = Logger.getLogger(RDFConnectionExample4.class);




      public static void main(String ...args) {

      log.setLevel(Level.INFO);
      log.info("This is Luis Logger");
BasicConfigurator.configure();



          String my_query = "PREFIX schema: <http://schema.org/>\n" +
      "PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>\n" +
      "PREFIX owl: <http://www.w3.org/2002/07/owl#>\n" +
      "PREFIX hist: <http://wikiba.se/history/ontology#>\n" +
      "PREFIX wd: <http://www.wikidata.org/entity/>\n" +
      "PREFIX wdt: <http://www.wikidata.org/prop/direct/>\n" +
      "PREFIX wikibase: <http://wikiba.se/ontology#>\n" +
      "PREFIX dct: <http://purl.org/dc/terms/>\n" +
      "\n" +
      "SELECT ?item1  WHERE {\n" +
      "    ?item1 wdt:P31 ?item2.\n" +
      "} LIMIT 10";

     System.out

.println("The query string is"+ my_query);

          Query query = QueryFactory.create(my_query);

          //method 1 with query execution

          QueryExecution qe1 = QueryExecutionFactory.sparqlService("
https://query.wikidata.org/sparql";, query);

          ResultSet rs1 = qe1.execSelect() ;

          while(rs1.hasNext()) {
              QuerySolution qs1 = rs1.next() ;
              Resource subject1 = qs1.getResource("s") ;
              System.out.println("Subject: "+subject1) ;
          }

          //method 2




           RDFConnection conn0 = RDFConnectionRemote.create()
              .destination("https://query.wikidata.org/";)
              .queryEndpoint("sparql")
              // Set a specific accept header; here, sparql-results+json
(preferred) and text/tab-separated-values
               //The default is "application/sparql-results+json,
application/sparql-results+xml;q=0.9, text/tab-separated-values;q=0.7,
text/csv;q=0.5, application/json;q=0.2, application/xml;q=0.2, */*;q=0.1"
             .acceptHeaderSelectQuery("application/sparql-results+json,
application/sparql-results+xml;q=0.9")
             .build();


          String queryService = "https://query.wikidata.org/sparql?";;

          RDFConnection conn = RDFConnectionFactory.connect(queryService,
null, null);

          QueryExecution qe2 = conn.query(query);

          ResultSet rs2 = qe2.execSelect() ;

          while(rs2.hasNext()) {
              QuerySolution qs2 = rs2.next() ;
              Resource subject2 = qs2.getResource("s") ;
              System.out.println("Subject: "+subject2) ;
          }



         // QueryExecution qExec = conn.query(query);


      }












https://jena.apache.org/documentation/rdfconnection/